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    are their any predicted questions that will defo come up lol if only i had the exam paper b4 hand sum hw :-)
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    (Original post by VetApplicant)
    I have a 50 slide revision powerpoint for OCR AS Biology last year
    If anyone wants it, just tell me how to send it and I will
    Could you send me this too? Please, please, please. please ? ;D
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    (Original post by qasidb)
    Aren't 7 and 8 the wrong way round?
    I thought the ventricles begin to contract pushing blood in the atrioventricular valve falps causing them to close.
    if the ventricles contracted while the valves was open the blood would return to the atria instead of going through the aorta to the body
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    (Original post by qasidb)
    Aren't 7 and 8 the wrong way round?
    I thought the ventricles begin to contract pushing blood in the atrioventricular valve falps causing them to close.
    AV valves shut at the end of atrial systole, just before ventricular systole. because at the end of atrial systole, blood has poured into ventricles, so volume of blood and pressure in atria starts to decrease, and the blood that has just flown into the ventricles starts to flow back into the atria, filling the AV valve pockets with blood and therefore closing them. the closing of the AV valves makes a sound, and after they are shut, ventricular systole begins.
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    (Original post by giraffegiraffe)
    AV shut at the end of atrial systole, just before ventricular systole. because at the end of atrial systole, blood has poured into ventricles, so volume of blood and pressure in atria starts to decrease, and the blood that has just flown into the ventricles starts to flow back into the atria, filling the AV valve pockets with blood and therefore closing them. the closing of the AV valves makes a sound, and after they are shut, ventricular systole begins.
    yh thts right
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    what do you think your going to get in the exam
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    (Original post by billy_h786)
    no coz u do tht in a2 i think lol
    the spec says you need to know it. breathing rate=number of peaks per minute
    oxygen uptake=decrease in peaks over a period of 1 minute
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    translocation- the movement of assimilates along the phloem
    sink- removal of sucrose in the phloem
    source- releases sucrose in the phloem

    HOW DOES SUCROSE ENTER THE PHLOEM?
    basically the companion cells actively pump H+ ions form their cytoplasm using ATP energy into the surrounding cells. This produces a diffusion gradient. therefore the h+ will diffuse in to the companion cells with sucrose from a rgion of high concentration to a region of low concentration down a diffusion gradient through cotransporter proteins. this increases the concentration of sucrose in the companion cells which then diffuse into the seive tube elements via the plasmodesmata.
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    Can anyone describe the function of the chordae tendineae in the heart and how they carry out the function
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    do we need to know specific stains for the microscopes topic? they arent really mentioned in the book..
    or just the fact that stains help some features of the image stand out, and dyes are used for light microscopes and metal particles are used for electron microscope stains to create contrast in the image?
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    (Original post by The Smeezington)
    Can anyone describe the function of the chordae tendineae in the heart and how they carry out the function
    i'm not sure that we need to know this in detail, just that the cords are on the inside of the valves and stop the valves from turning inside out therefore stop blood flowing the wrong way?
    correct me if i'm wrong someone!
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    there's a thread on phloem/translocation etc here


    http://www.thestudentroom.co.uk/show...ghlight=phloem
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    (Original post by The Smeezington)
    Can anyone describe the function of the chordae tendineae in the heart and how they carry out the function
    they are connected to the walls of the inside cardiac muscle. The have a small piece of tissue which contracts the same one of the atria or ventricles contract to open or close the valve e.g. when the ventricles contract it also contracts to close the valve and when the atria contracts it relaxes
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    ok.....i'm stealing notes from this thread....the Edexcel one sucks !
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    (Original post by giraffegiraffe)
    do we need to know specific stains for the microscopes topic? they arent really mentioned in the book..
    or just the fact that stains help some features of the image stand out, and dyes are used for light microscopes and metal particles are used for electron microscope stains to create contrast in the image?
    in light microscopes colour stains chemicaly bind to parts of the cellular structure to show e.g. organelles. Different stains bind to different structures in a cell.

    A lead or salt stain must be used in a electron microscope to scatter the electrons and create contrast
    hope it helps
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    can anyone describe what happens during G1,G2 and S1 during interphase?
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    can sum1 explain microtubules please
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    Look at graph:
    http://www.enotes.com/w/images/thumb..._Ventricle.PNG


    does this show that the electrical activity of the heart is directly related to the cardiac cycle. how.
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    (Original post by billy_h786)
    in light microscopes colour stains chemicaly bind to parts of the cellular structure to show e.g. organelles. Different stains bind to different structures in a cell.

    A lead or salt stain must be used in a electron microscope to scatter the electrons and create contrast
    hope it helps
    perfect thankyou!
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    (Original post by ayesha00)
    can anyone describe what happens during G1,G2 and S1 during interphase?
    G1 - protein syntheis and the groth of proteins and organells
    S1 - is the replication of chromosomes
    G2 - is the growth of the cell and the growth of the spindle fibres
 
 
 
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